Optical switch element comprising a liquid-crystalline medium

ABSTRACT

The present invention relates to an optical switch element, comprising a liquid-crystalline medium for the temperature-dependent regulation of radiant energy flow. The invention furthermore relates to the use of the optical switch element for the regulation of radiant energy flow between interior spaces and the environment and for the regulation of the temperature of interior spaces. The invention furthermore relates to a liquid-crystalline medium, characterised in that it comprises 5-95% of a compound of the formula (I), in particular for use in the optical switch elements according to the invention.

The present invention relates to a thermoresponsive optical switchelement, comprising a liquid-crystalline medium for thetemperature-dependent regulation of radiant energy flow. The inventionfurthermore relates to the use of the optical switch element for theregulation of radiant energy flow between interior spaces and theenvironment and for the regulation of the temperature of interiorspaces. The invention furthermore relates to a liquid-crystallinemedium, characterised in that it comprises 5-95% of a compound of theformula (I), in particular for use in the switch elements mentionedabove.

The optical switch element is used in accordance with the invention inwindows or comparable openings in buildings, such as, for example, inglazed doors, skylights and/or glass roofs for the regulation of lightinflux.

For the purposes of this invention, the term liquid-crystalline mediumis to be taken to mean a material or compound which under certainconditions shows liquid-crystalline properties. Preferably, theliquid-crystalline medium shows thermotropic behavior, more preferably,the liquid-crystalline medium exhibits a temperature-induced phasetransition from an isotropic to a liquid-crystalline phase, mostpreferably to a nematic phase.

For the purposes of this invention, the term interior space is intendedto be taken to mean both interior spaces in private, public orcommercial buildings, for example buildings used for office purposes,and also the interior spaces of vehicles. Furthermore, the term interiorspace is also intended to be taken to mean the interior spaces ofbuildings used purely commercially, such as, for example, greenhouses.

For the purposes of this invention, the term window is intended to betaken to mean any desired light-transmissive openings sealed by solidmaterial in buildings, in transport containers or in vehicles.

For the purposes of this invention, radiant energy flow is taken to meanthe flow of electromagnetic radiation which emanates from the sun, hitsthe earth after passing through the atmosphere and is only absorbed to asmall extent, or not at all, by glass sheets. The electromagneticradiation may alternatively also emanate from light sources other thanthe sun. Since relatively short-wavelength radiation (UV-B light) andlong-wavelength infrared radiation are absorbed by the atmosphere or byglass sheets, for the purposes of this invention, the term “radiantenergy” is understood to comprise UV-A light, light in the visibleregion (VIS light) and near-infrared (NIR) light.

The term light, unless defined more precisely, is likewise intended tobe taken to mean electromagnetic radiation in the UV-A region, VISregion and near-infrared region.

According to commonly used definitions in the field of physical optics,for the purposes of this invention, UV-A-light is understood to beelectromagnetic radiation of 320 to 380 nm wavelength. VIS-light isunderstood to be electromagnetic radiation of 380 to 780 nm wavelength.Near-infrared light (NIR) is understood to be electromagnetic radiationof 780 to 3000 nm wavelength.

Therefore, for the purposes of this invention, the terms “radiantenergy” and “light” are understood to be electromagnetic radiation of320 to 3000 nm wavelength.

For the purposes of this invention, the term optical switch element thusdenotes a device capable of switching between a state in which it haslower transmission for radiant energy and a state in which it has highertransmission for radiant energy, the term radiant energy being definedas above. The switch element may selectively switch in one or moresub-regions of the spectrum of radiant energy. The terms “device” and“switch element” are being used interchangeably in the following.

The optical switch element according to the invention isthermoresponsive. However, it may additionally also be controlled by oneor more other mechanisms, for example by electrical current ormechanical mechanisms. Preferably, such other mechanisms are notpresent.

Modern buildings are distinguished by a high proportion of glasssurfaces, which is desired both for aesthetic reasons and also inrelation to the brightness and comfort of the interior spaces. It hasbecome equally important in recent years that buildings used for livingor commercial purposes and/or which are accessible to the public havehigh energy efficiency. This means that as little energy as possible hasto be expended for heating purposes in the cold season in temperateclimatic zones (where the majority of highly developed industrialnations are located) and no or only little air conditioning of theinterior spaces is necessary in the warm season.

However, a high proportion of glass surfaces hinders the achievement ofthese aims. In warm climatic zones and in the warm season in temperateclimatic zones, glass surfaces result in undesired heating of theinterior spaces when they are hit by solar radiation. This is due to thefact that glass is transparent to radiation in the VIS and NIR region ofthe electromagnetic spectrum. Objects in the interior space absorb theradiation that is allowed through and are warmed thereby, which resultsin an increase in the temperature of the interior space (greenhouseeffect).

This increase in temperature of the interior space behind a glasssurface which is called greenhouse effect is due to the fact that theobjects in the interior which have absorbed the radiation will also emitradiation. However, the emitted radiation of these objects is mainly inthe infrared spectrum (typically about 10,000 nm wavelength) of light.It therefore cannot pass through the glass again and is “trapped” in thespace behind the glazing.

However, the above-described effect of glass surfaces in buildings isnot generally undesired: at low outside temperatures, in particular incold climatic zones or in the cold season in temperate climatic zones,heating of the interior spaces owing to solar radiation due to thegreenhouse effect may be advantageous since the energy requirement forheating is thereby reduced and costs can thus be saved.

With the increasing importance of energy efficiency of buildings, thereis therefore a growing demand for devices which control the flow ofenergy through windows or glass surfaces. In particular, there is ademand for devices which enable the flow of energy through glasssurfaces to be matched to the conditions (heat, cold, high solarradiation, low solar radiation) prevailing at the particular time.

Of particular interest is the provision of such devices in temperateclimatic zones, in which a seasonal change occurs between warm outsidetemperatures combined with high solar radiation and cold outsidetemperatures combined with low solar radiation.

The prior art discloses both non-switchable devices, which limit theenergy flow, but cannot be adapted in a variable manner, and alsoswitchable devices, which are able to match the energy flow to therespective conditions prevailing. Amongst the switchable devices, adistinction should be made between devices which do not adaptautomatically to the ambient conditions and devices which adaptautomatically to the ambient conditions. The latter devices are alsoknown as smart windows.

In order to improve the thermal insulation of windows, multiple-glazedwindow units (insulated glass units, IGU) have been known for some time.The sequence of two or more glass panes which enclose one or moregas-filled interspaces which are insulated from the environment enablesthermal conduction through windows to be significantly reduced comparedwith single-glass panes.

The prior art furthermore discloses the coating of glass surfaces withthin metal or metal-oxide layers. The production of glass coated in thisway is disclosed, for example, in, inter alia, U.S. Pat. No. 3,990,784and U.S. Pat. No. 6,218,018. The coating of glass surfaces with thinmetal or metal-oxide layers is in many cases combined with the use ofmultipane insulating glass. The coating has the effect, inter alia, thatthe transparency of the glass to near-infrared radiation is reduced,thus reducing the heating of the interior space owing to the greenhouseeffect.

If the radiant energy flow is controlled exclusively by a coatingtechnique of this type and/or by the use of insulating glass, however,adaptation to varying weather or seasonal conditions is not possible.For example, it would be of interest for windows to be totallytransparent to sunlight at cold outside temperatures in order to reducethe energy consumption for heating. Conversely, it would be desirablefor windows to allow less sunlight to pass through at warm outsidetemperatures, so that less heating of the interior spaces takes place.

There is therefore a demand for devices in which the radiant energy flowcan be matched to the respective conditions prevailing. In particular,there is a demand for devices which are able to adapt automatically tothe ambient conditions.

The prior art discloses devices which, on application of an electricalvoltage, can be switched reversibly from a light-transmissive state to aless light-transmissive state, which can either be a light-scatteringstate or a state in which less light is transmitted, but transparency ismaintained.

The first state will be referred to as bright state in the following,whereas the second state will be referred to as dark state.

A differentiation shall be made within the dark state between a darkstate in which the device scatters incoming light and is thereforemerely translucent and not transparent anymore and a dark state in whichthe device is less light-transmissive but still transparent. The formerwill be referred to as a dark translucent state, whereas the latter willbe referred to as a dark transparent state.

Therefore, two types of switch elements can be discerned: those whichswitch between a bright state and a dark transparent state and thosewhich switch between a bright state and a dark translucent state.Representatives for both types of switch elements are known in the priorart.

A possible embodiment of electrically switchable devices areelectrochromic devices, which are presented, inter alia, in Seeboth etal., Solar Energy Materials & Solar Cells, 2000, 263-277. A furtherreview is offered by C. M. Lampert et al., Solar Energy Materials &Solar Cells, 2003, 489-499. The electrically switchable devicespresented therein can typically be switched between a bright state and adark transparent state.

U.S. Pat. No. 7,042,615 and U.S. Pat. No. 7,099,062 describe, forexample, electrochromic devices in which the switching between atransparent state and a non-transparent state is achieved by theapplication of a voltage and the resulting migration of ions.

Further electrically switchable devices known from the prior art for thecontrol of radiant energy flow are devices based on suspended particles(suspended particle devices, SPDs), for example particles of organicpolyiodides, which align in an electrical field (U.S. Pat. No.4,919,521). They likewise typically switch from a bright state to a darktransparent state.

Further electrically switchable devices known from the prior art arebased on the alignment of molecules of a liquid-crystalline medium onapplication of an electric field.

Such devices are disclosed, inter alia, in U.S. Pat. No. 4,268,126, U.S.Pat. No. 4,641,922, U.S. Pat. No. 5,940,150 and WO 2008/027031 andlikewise switch under electrical control from a bright state to a darktransparent state.

Although the electrically switchable devices mentioned above enable theradiant energy flow to be set, they have the disadvantage of having tobe electrically controlled.

It would be desirable to have available a switch element which adaptsautomatically to the ambient conditions and which does not have to becontrolled either manually or by any additional coupled device capableof giving a signal upon a detected temperature deviation.

It would furthermore be desirable to have available a switch elementwhich does not require any electrical circuits. The introduction ofelectrical circuits into windows is accompanied by additional workduring manufacture of the windows and entails the risk of susceptibilityto flaws or a short service life of the devices. Furthermore, additionalinfrastructure is necessary for such devices, including electrical powersupply.

Devices which are not electrically switched, but instead are, forexample, temperature-controlled (thermoresponsive devices), aredescribed, inter alia, in Nitz et al., Solar Energy 79, 2005, 573-582. Apossible embodiment of such devices are systems which are based on theseparation between two phases above a certain temperature. Furtherembodiments are based on temperature-dependent properties of hydrogels.However, these devices typically switch between a transparent state anda dark translucent state, which is undesired for applications in whichit is required that the device stays transparent also in the dark state.

US 2009/0015902 and US 2009/0167971 disclose optical switch elementscomprising a liquid-crystalline medium between two polarisers. Theliquid-crystalline medium has the property of rotating the plane ofpolarisation of the light at a first temperature and not rotating oressentially not rotating the plane of polarisation of the light at asecond temperature. Thus, a suitable arrangement of the polarisersenables the devices to allow more light to pass through at the firsttemperature than at the second temperature. The twotemperature-dependent states represent a bright state (firsttemperature) and a dark transparent state (second temperature).

In particular, the two applications US 2009/0015902 and US 2009/0167971disclose devices in which a twisted nematic cell (TN cell) is used asoptical switch element. In this case, the switching between the brightstate and the dark transparent state is achieved by the phase transitionof the liquid-crystalline medium present in the twisted nematic cellfrom a nematic state at a temperature below the clearing point to anisotropic state at a temperature above the clearing point.

In the twisted nematic cells, the plane of polarisation of the secondpolariser is rotated with respect to the plane of polarisation of thefirst polariser by a defined value. Furthermore, in the nematic state,the liquid-crystalline medium rotates the plane of polarisation ofpolarised light by a defined value which may be different from thebefore-mentioned value. In the isotropic state, the liquid-crystallinemedium does not rotate the plane of polarisation of polarised light.

According to a preferred embodiment disclosed in US 2009/0015902 and US2009/0167971, the two polarisers are arranged to each other in such away that a defined amount of light can pass through the combination offirst polariser, liquid-crystalline medium in its nematic state andsecond polariser. This state of the device, in which theliquid-crystalline medium is nematic, represents the bright state of thedevice.

When the liquid-crystalline medium changes from the liquid-crystallineto the isotropic state, less light can pass through the device. Thisstate of the device, in which the liquid-crystalline medium isisotropic, represents the dark state of the device.

The applications US 2009/0015902 and US 2009/0167971 furthermoredisclose that liquid-crystalline media having a low clearing point aresuitable for use in the said devices. The switching process from thebright state to the dark transparent state, which is caused by the phasetransition of the liquid-crystalline medium, is intended to take placemerely on heating of the device by the typical radiation intensity ofthe sun in the warm season. To this end, a preferred clearing point ofbelow 85° C. is disclosed. An example disclosed is a liquid-crystallinemedium which comprises the liquid-crystalline mixture E7 together withadded 4′-hexyl-4-cyanobiphenyl (6CB) and which has a clearing point of35° C. It is furthermore generally disclosed in the above-mentionedapplications that the liquid-crystalline mixture ZL11132 (Merck KGaA)with a clearing point of 72° C. can alternatively also be used as thebasis for the preparation of liquid-crystalline media for use in theswitchable devices. However, no specific illustrative embodiments aredisclosed in this respect.

In this respect, it is to be noted that the modification of mixture E7disclosed in US 2009/0015902 and US 2009/0167971 by addition ofalkylcyanobiphenyl compounds, such as, for example,4′-hexyl-4-cyanobiphenyl, has the disadvantage that the low-temperaturestability of the liquid-crystalline medium is impaired.

A good low-temperature stability of the liquid-crystalline medium ishowever highly desirable, since in many applications, the switch elementis exposed to low temperatures for extended periods of time.

There continues to be a demand for liquid-crystalline media which aresuitable for use in thermally switchable devices. In particular, thereis a demand for liquid-crystalline media which have a transition from anematic state to an isotropic state (clearing point) at a temperaturewhich is within the operating-temperature range of the optical switchelement. There is furthermore a demand for liquid-crystalline mediawhich have a high content of mixed cycloaliphatic and aromatic two-ringcompounds, since such two-ring compounds can be preparedcost-effectively. There is furthermore a demand for liquid-crystallinemedia which have good low-temperature storage stability, preferably incombination with the properties mentioned above.

To this end, the present invention provides a thermoresponsive opticalswitch element comprising a liquid-crystalline medium, which comprisesone or more compounds of the formula (I)

where

-   R¹¹,R¹² are on each occurrence, identically or differently, selected    from an alkyl, alkoxy or thioalkoxy group having 1 to 10 C atoms or    an alkenyl, alkenyloxy or thioalkenyloxy group having 2 to 10 C    atoms, where one or more H atoms in the groups mentioned above may    be replaced by F or Cl and where one or more CH₂ groups may be    replaced by O or S, or are selected from the group comprising F, Cl,    CN, NCS, R¹—O—CO— and R¹—CO—O—; where-   R¹ is, identically or differently on each occurrence, an alkyl or an    alkenyl group having 1 to 10 C atoms, in which one or more H atoms    may be replaced by F or Cl; and

is selected from

is selected from

and

-   Z¹¹ is selected from —CO—O— and —O—CO—; and-   X is on each occurrence, identically or differently, F, Cl, CN or an    alkyl, alkoxy or thioalkoxy group having 1 to 10 C atoms, where one    or more H atoms in the groups mentioned above may be replaced by F    or Cl and where one or more CH₂ groups may be replaced by O or S;    and-   Y is on each occurrence, identically or differently, selected from H    and X.

Preferentially, the liquid-crystalline medium furthermore comprises oneor more compounds of the formula (II)

whereR²¹,R²² have the meanings indicated for R¹¹ and R¹² above; and

are, identically or differently, selected from

where X and Y are defined as above; and

-   Z²¹ is selected from —CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —CH₂CH₂—,    —OCH₂—, —CH₂O— and a single bond;    with the proviso that if one of

and Z²¹ is selected from —CO—O— and —O—CO—,the other one of

must not be selected from

with X and Y being defined as above.

Preferentially, the liquid-crystalline medium furthermore comprises oneor more compounds selected from compounds of the formulas (III) and (IV)

whereR³¹,R³²,R⁴¹ and R⁴² have the meanings indicated for R¹¹ and R¹² above;and

are on each occurrence, identically or differently, selected from

where X and Y are defined as above; and

are on each occurrence, identically or differently, selected from

andwhere X and Y are defined as above; and

-   Z³¹ and Z³² are on each occurrence, identically or differently,    selected from —CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —CH₂CH₂—, —OCH₂—,    —CH₂O— and a single bond; and-   Z⁴¹, Z⁴² and Z⁴³ are on each occurrence, identically or differently,    selected from —CO—O—, —O—CO— and a single bond.

According to a preferred embodiment of the invention, theliquid-crystalline medium comprises one or more compounds of formula (I)and one or more compounds of formula (II) and one or more compoundsselected from compounds of the formulas (III) and (IV), as definedabove.

According to a preferred embodiment of the invention, X is, identicallyor differently on each occurrence, selected from F, Cl, CN and an alkylgroup having 1 to 8 C atoms. It is particularly preferred that X isselected from F and Cl, and it is very particularly preferred that X isF.

Furthermore, it is preferred that R¹¹ and R¹² are on each occurrence,identically or differently, selected from a straight-chain alkyl oralkoxy group having 1 to 10 C atoms and an alkenyl or alkenyloxy grouphaving 2 to 10 C atoms, where one or more H atoms in the groupsmentioned above may be replaced by F or Cl, or are selected from thegroup comprising F, Cl, CN, R¹—O—CO— and R¹—CO—O—; where R¹ is definedas above.

For compounds according to formula (I), it is preferred that R¹¹ isselected from a straight-chain alkyl or alkoxy group having 1 to 10 Catoms, R¹—O—CO— and R¹—CO—O—; where R¹ is defined as above.

For compounds according to formula (I), it is furthermore preferred thatR¹² is a straight-chain alkyl or alkoxy group having 1 to 10 C atoms,where one or more H atoms in the groups mentioned above may be replacedby F or Cl or that R¹² is selected from F, Cl, R¹—O—CO— and R¹—CO—O—;where R¹ is defined as above.

For compounds according to formula (I), it is furthermore preferred thatZ¹¹ is —CO—O—.

According to a further preferred embodiment,

is equal to

According to a particularly preferred embodiment of the invention,compounds according to formula (I) are compounds of the followingformulas (I-1) and (I-2):

where R¹¹, R¹² and X are defined as above.

According to an even more preferred embodiment, compounds according toformula (I-1) are compounds of the following formulas (I-1a) to (I-1b)

where R¹¹ and R¹² are, identically or differently on each occurrence, analkyl group having 1 to 10 C atoms, andR¹ is an alkyl group having 1 to 10 C atoms, in which one or more Hatoms may be replaced by F or Cl.

According to a further even more preferred embodiment, compoundsaccording to formula (I-2) are compounds of the following formula (I-2a)

where R¹¹ is an alkyl group having 1 to 10 C atoms, andR¹ is an alkyl group having 1 to 10 C atoms.

According to a preferred embodiment, in compounds according to formula(II),

is selected from

is selected from

where X is defined as above,with the proviso that if one of

and Z²¹ is selected from —CO—O— and —O—CO—,the other one of

must not be selected from

with X being defined as above.

According to a further preferred embodiment, Z²¹ is —CO—O— or a singlebond.

According to a further preferred embodiment, R²¹ and R²² are,identically or differently on each occurrence, F, Cl, CN or an alkyl oralkoxy group having 1 to 10 C atoms, in which one or more H atoms may bereplaced by F or Cl or an alkenyl group having 2 to 10 C atoms.

According to a particularly preferred embodiment, compounds according toformula (II) are compounds of the following formulas (II-1) to (II-2)

where R²¹, R²²,

are defined as above,with the proviso that, for compounds according to formula (II-1), if oneof

the other one of

must not be selected from

with X and Y being defined as above.

According to a preferred embodiment, in compounds according to formula(II-1),

is equal to

whereX is defined as above.

According to a further preferred embodiment, in compounds according toformula (II-2),

whereX is defined as above.

Particularly preferred embodiments of compounds according to formula(II-1) are compounds of the following formulas (II-1a) to (II-1d)

where R¹, R²¹ and R²² are defined as above.

According to a preferred embodiment, in compounds according to formulas(II-1a) to (II-1d), R¹, R²¹ and R²² are, identically or differently oneach occurrence, an alkyl group having 1 to 10 C atoms.

Particularly preferred embodiments of compounds according to formula(II-2) are compounds of the following formulas (II-2a) to (II-2g)

where R¹, R²¹ and R²² are defined as above.

According to a preferred embodiment, in compounds according to formulas(II-2a) to (II-2g), R¹, R²¹ and R²² are, identically or differently oneach occurrence, an alkyl group having 1 to 10 C atoms.

According to a further preferred embodiment, in compounds according toformula (III),

are on each occurrence, identically or differently, selected from

whereX is defined as above.

According to a further preferred embodiment, in compounds according toformula (III),

Z³¹ and Z³² are, identically or differently on each occurrence, —CO—O—,—O—CO—, —CH₂—CH₂— or a single bond.

According to a further preferred embodiment, in compounds according toformula (III), R²¹ and R²² are, identically or differently on eachoccurrence, F, Cl or CN or an alkyl group having 1 to 10 C atoms, inwhich one or more H atoms may be replaced by F or Cl.

According to a particularly preferred embodiment, compounds according toformula (III) are compounds of the following formulas (III-1) to (III-3)

where the groups R³¹, R³², Z³¹, Z³² and

are defined as above.

According to a preferred embodiment, in compounds according to formula(III-1),

are on each occurrence, identically or differently, selected from

whereX is defined as above.

According to a further preferred embodiment, in compounds according toformula (III-2),

are on each occurrence, identically or differently, selected from

According to a further preferred embodiment, in compounds according toformula (III-3),

are on each occurrence, identically or differently, selected from

whereX is defined as above.

According to a particularly preferred embodiment of the invention,compounds of the formula (III-1) are compounds of the following formulas(III-1a) to (III-1e)

where R³¹ and R³² are defined as above.

According to a particularly preferred embodiment of the invention, incompounds according to formulas (III-1a) to (III-1e), R³¹ and R³² are,identically or differently on each occurrence, an alkyl group having 1to 10 C atoms.

According to a further particularly preferred embodiment of theinvention, compounds of the formula (III-2) are compounds of thefollowing formula (III-2a)

where R³¹ is defined as above.

According to a particularly preferred embodiment of the invention, incompounds according to formula (III-2a), R³¹ is an alkyl group having 1to 10 C atoms.

According to a further particularly preferred embodiment of theinvention, compounds of the formula (III-3) are compounds of thefollowing formulas (III-3a) to (III-3c)

are on each occurrence, identically or differently, selected from

whereX is defined as above, and R³¹ and R³² are defined as above.

According to a most preferred embodiment of the invention, compounds ofthe formula (III-3a) are compounds of the following formulas (III-3a-1)to (III-3a-6)

where R³¹ and R³² are defined as above.

Preferably, in compounds according to formulas (III-3a-1) to (III-3a-6),R³¹ and R³² are, identically or differently on each occurrence, an alkylgroup having 1 to 10 C atoms.

According to a further most preferred embodiment of the invention,compounds of the formula (III-3b) are compounds of the following formula(III-3b-1)

where R³¹ and R³² are defined as above.

Preferably, in compounds according to formula (III-3b-1), R³¹ and R³²are, identically or differently on each occurrence, an alkyl grouphaving 1 to 10 C atoms.

According to a further most preferred embodiment of the invention,compounds of the formula (III-3c) are compounds of the followingformulas (III-3c-1) to (III-3c-3)

where R³¹ and R³² are defined as above.

Preferably, in compounds according to formula (III-3c-1) to (III-3c-3),R³¹ and R³² are, identically or differently on each occurrence, an alkylgroup having 1 to 10 C atoms, in which one or more H atoms may bereplaced by F or Cl.

According to a further preferred embodiment, in compounds according toformula (IV),

are on each occurrence, identically or differently, selected from

whereX is defined as above.

According to a further preferred embodiment, in compounds according toformula (IV),

Z⁴¹ to Z⁴³ are, identically or differently on each occurrence, —CO—O— ora single bond.

According to a further preferred embodiment, in compounds according toformula (IV),

R⁴¹ and R⁴² are, identically or differently on each occurrence, an alkylgroup having 1 to 10 C atoms.

According to a preferred embodiment of the invention, compoundsaccording to formula (IV) are compounds of the following formulas (IV-1)and (IV-2)

where R⁴¹ and R⁴² and

are defined as above.

According to a particularly preferred embodiment of the invention,compounds according to formula (IV-1) are compounds of the followingformulas (IV-1a) to (IV-1b)

where R⁴¹ and R⁴² are defined as above.

According to a preferred embodiment, R⁴¹ and R⁴² in formulas (IV-1a) to(IV-1b) are, identically or differently on each occurrence, an alkylgroup having 1 to 10 C atoms.

According to a further particularly preferred embodiment of theinvention, compounds according to formula (IV-2) are compounds of thefollowing formula (IV-2a)

where R⁴¹ and R⁴² are defined as above.

According to a preferred embodiment, R⁴¹ and R⁴² in formula (IV-2a) are,identically or differently on each occurrence, an alkyl group having 1to 10 C atoms.

According to a preferred embodiment of the invention, the totalconcentration of the compounds of formula (I) is between 5 and 95%. Morepreferably, the concentration of the compounds according to formula (I)is between 6 and 60%, most preferably between 7 and 55%.

It is furthermore preferred that the total concentration of thecompounds of formula (II) is between 1 and 75%. More preferably, theconcentration of the compounds according to formula (II) is between 10and 75%, even more preferably between 20 and 55% and most preferablybetween 30 and 75%.

It is furthermore preferred that the total concentration of compoundsaccording to formula (II-2g) is between 0 and 40%, more preferablybetween 0 and 30%, and most preferably between 0 and 25%.

It is furthermore preferred that the total concentration of thecompounds of the formulas (I) and (II) is between 40 and 100%. Morepreferably, it is between 50 and 100%, most preferably, it is between 70and 100%.

It is furthermore preferred that the total concentration of thecompounds of the formulas (III) and (IV) is between 0 and 30%.

The invention concerns furthermore a liquid-crystalline mediumcomprising one or more compounds of the formula (I) as defined above ina total concentration of 5 to 95% and at least one further compound ofthe formula (II) as defined above, so that the total concentration ofthe compounds of the formulas (I) and (II) is between 40 and 100%.

According to a preferred embodiment of the invention, theliquid-crystalline medium comprises at least 5 different compoundsselected from the compounds of formulas (I) to (IV). According to aparticularly preferred embodiment, the liquid-crystalline mediumcomprises at least 6 different compounds selected from the compounds offormulas (I) to (IV). According to an even more preferred embodiment,the liquid-crystalline medium comprises at least 7 different compoundsselected from the compounds of formulas (I) to (IV).

Optionally the media according to the present invention may comprisefurther liquid crystal compounds in order to adjust the physicalproperties. Such compounds are known to the expert. Their concentrationin the media according to the instant invention is preferably 0% to 30%,more preferably 0.1% to 20% and most preferably 1% to 15%.

The liquid crystal media according to the present invention may containchiral dopants as further additives in usual concentrations. Preferredchiral dopants are listed in Table E below. The total concentration ofthese further constituents is in the range of 0% to 10%, preferably 0.1%to 6%, based on the total mixture. The concentrations of the individualcompounds used each are preferably in the range of 0.1% to 3%. Theconcentration of these and of similar additives is not taken intoconsideration for the values and ranges of the concentrations of theliquid crystal components and compounds of the liquid crystal media inthis application.

The liquid crystalline media according to the present invention maycontain dyes as further additives in usual concentrations. In apreferred embodiment, dyes or combinations of dyes leading to grey orblack color are used. In a further preferred embodiment, the dyes areselected from dyes with high light stability and good solubility, e.g.azo-dyes or anthraquinone dyes. The total concentration of these furtherconstituents is in the range of 0% to 10%, preferably 0.1% to 6%, basedon the total mixture. The concentrations of the individual compoundsused each are preferably in the range of 0.1% to 9%. The concentrationsof these and of similar additives is not taken into consideration forthe values and ranges of the concentrations of the liquid crystalcomponents and compounds of the liquid crystal media in thisapplication.

The liquid crystalline media according to the invention may containstabilizers as further additives in usual concentrations. Preferredstabilizers are listed in Table F below. The total concentration of thestabilizers is in the range of 0% to 10%, preferably 0.0001% to 1%,based on the total mixture.

According to a preferred embodiment of the invention, the clearing point(the temperature of the phase transition from the nematic to theisotropic state, T(N,I)) is lower than 60° C. According to aparticularly preferred embodiment, T(N,I) is lower than 50° C. Accordingto an even more preferred embodiment, T(N,I) is lower than 40° C., andmost preferably lower than 30° C.

A preferred liquid-crystalline medium for use in the thermoresponsiveoptical switch element according to the invention comprises (preferredliquid-crystalline medium I)

-   -   one or more compounds according to formulas (I-1a), (I-1b) or        (I-2a) in a total concentration of 5 to 95%,    -   one or more compounds according to formula (II-2g) in a total        concentration of 1 to 40%,    -   one or more compounds according to formulas (II-2c) to (II-2f)        or (II-1a) to (II-1d) in a total concentration of 0 to 70%, and    -   one or more compounds according to formulas (III-1a) to        (III-1e), (III-2a), (III-3a-1) to (III-3a-6), (III-3b-1),        (III-3c-1) to (III-3c-3), (IV-1a) to (IV-1b) and (IV-2a) in a        total concentration of 0 to 30%, and        where the total concentration of the compounds of the        formulas (I) and (II) is between 40 and 100%.

In another preferred embodiment of the invention, the liquid-crystallinemedium comprises (preferred liquid-crystalline medium II)

-   -   one or more compounds according to formulas (I-1a), (I-1b) or        (I-2a) in a total concentration of 5 to 95%    -   one or more compounds according to formulas (II-2c) to (II-2f)        in a total concentration of 0 to 70%,    -   one or more compounds according to formula (II-1a) to (II-1d) in        a total concentration of 1 to 70%, and    -   one or more compounds according to formulas (III-1a) to        (III-1e), (III-2a), (III-3a-1) to (III-3a-6), (III-3b-1),        (III-3c-1) to (III-3c-3), (IV-1a) to (IV-1b) and (IV-2a) in a        total concentration of 0 to 30%, and        where the total concentration of the compounds of the        formulas (I) and (II) is between 40 and 100%.

In another preferred embodiment of the invention, the liquid-crystallinemedium comprises (preferred liquid-crystalline medium III)

-   -   one or more compounds according to formulas (I-1a), (I-1b) or        (I-2a) in a total concentration of 5 to 95%    -   one or more compounds according to formulas (II-2a) to (II-2f)        in a total concentration of 5 to 70%,    -   one or more compounds according to formulas (III-1a) to        (III-1e), (III-2a), (III-3a-1) to (III-3a-6), (III-3b-1),        (III-3c-1) to (III-3c-3), (IV-1a) to (IV-1b) and (IV-2a) in a        total concentration of 0 to 30%, and        where the total concentration of the compounds of the        formulas (I) and (II) is between 40 and 100%.

In another preferred embodiment of the invention, the liquid-crystallinemedium comprises (preferred liquid-crystalline medium IV)

-   -   one or more compounds according to formulas (I-1a), (I-1b) or        (I-2a) in a total concentration of 5 to 95%    -   one or more compounds according to formulas (II-2c) to (II-2f)        in a total concentration of 5 to 70%,    -   one or more compounds according to formulas (III-1a) to        (III-1e), (III-2a), (III-3a-1) to (III-3a-6), (III-3b-1),        (III-3c-1) to (III-3c-3), (IV-1a) to (IV-1b) and (IV-2a) in a        total concentration of 0 to 30%, and        where the total concentration of the compounds of the        formulas (I) and (II) is between 40 and 100%.

The liquid crystal media according to the present invention consist ofseveral compounds, preferably of 5 to 30, more preferably of 6 to 20 andmost preferably of 6 to 16 compounds. These compounds are mixedaccording to methods known in the art. As a rule, the required amount ofthe compound used in the smaller amount is dissolved in the compoundused in the greater amount. In case the temperature is above theclearing point of the compound used in the higher concentration, it isparticularly easy to observe completion of the process of dissolution.It is, however, also possible to prepare the media by other conventionalways, e.g. using so called pre-mixtures, which can be e.g. homologous oreutectic mixtures of compounds or using so called multi-bottle-systems,the constituents of which are ready to use mixtures themselves.

The invention concerns furthermore a process for the preparation of aliquid-crystalline medium as defined above, characterized in that one ormore compounds of the formula (I) are mixed with one or more compoundsof the formula (II) and optionally with one or more further mesogeniccompounds and/or additives.

According to a preferred embodiment of the invention, the optical switchelement comprises

-   -   the liquid-crystalline medium in the form of a thin layer, and    -   at least two polarisers, preferably in the form of thin layers,        one of them positioned on one side of the layer of the        liquid-crystalline medium, the other positioned on the opposite        side of the layer of the liquid-crystalline medium.

The polarisers can be linear or circular polarisers, preferably linearpolarisers.

For linear polarisers, it is preferred that the directions ofpolarisation of the two polarisers are rotated with respect to eachother by a defined angle.

Further layers and/or elements, such as one or more separate alignmentlayers, one or more glass sheets, one or more bandblock filters and/orcolor filters to block light of certain wavelengths, for exampleUV-light, may be present. Furthermore, one or more insulating layers,such as low-emissivity films, for example, may be present. Additionally,one or more adhesive layers, one or more protective layers, one or morepassivation layers and one or more barrier layers may be present.Optionally, a metal oxide layer, where the metal oxide may comprise twoor more different metals and where the metal oxide may be doped withhalogenide ions, preferably fluoride, may be present. Preferred is ametal oxide layer comprising one or more of the following: indium tinoxide (ITO), antimony tin oxide (ATO), aluminium zinc oxide (AZO), SnO₂and SnO₂:F (fluorine doped SnO₂). Particularly preferred is a metaloxide layer comprising ITO.

In the layer of the liquid crystalline medium, spacers may be present.Typical embodiments of the above-mentioned elements as well as theirfunction is known to the person skilled in the art.

For the purposes of this application, the term “polariser” refers to adevice or substance which blocks light of one polarisation direction andtransmits light of another polarisation direction. Likewise, the term“polariser” refers to a device or substance which blocks light of onekind of circular polarisation (right-handed or left-handed) whereas ittransmits light of the other kind of circular polarisation (left-handedor right-handed).

The blocking may occur by reflection and/or absorption. A reflectivepolariser therefore reflects light of one polarisation direction or onekind of circular polarisation and transmits light of the oppositepolarisation direction or other kind of circular polarisation; and anabsorptive polariser absorbs light of one polarisation direction or onekind of circular polarisation and transmits light of the oppositepolarisation direction or other kind of circular polarisation. Thereflection or absorption is typically not quantitative, leading to thepolarisation of light by the polariser not being perfect.

According to the present invention, both absorptive and reflectivepolarisers may be used in the optical switch elements. Preferably, thepolarisers according to the invention represent optical thin films.Examples of reflective polarisers which can be used according to theinvention are DRPF (diffusive reflective polariser film, by 3M), DBEF(dual brightness enhanced film, by 3M), layered-polymer distributedBragg reflectors (DBR) as described in U.S. Pat. No. 7,038,745 and U.S.Pat. No. 6,099,758 and APF (advanced polariser film, by 3M).Furthermore, wire-grid-polarisers (WGP), which reflect infrared light,as described in U.S. Pat. No. 4,512,638, for example, may be used.Wire-grid polarizers which reflect in the visible and ultraviolet partof the spectrum are described in U.S. Pat. No. 6,122,103, for example,and may also be used according to the invention. Examples of absorptivepolarisers which may be used according to the invention are Itos XP38polarising film or Nitto Denko GU-1220DUN polarising film. Examples ofcircular polarisers which can be used according to the invention areAPNCP37-035-STD (left handed) and APNCP37-035-RH (right handed) fromAmerican Polarizers Inc.

According to the invention, the optical switch element isthermoresponsive, signifying that its switching state is determined bytemperature. In a preferred embodiment of the invention, no electricalwiring, circuitry and/or switching network is present in the opticalswitching element.

The switching of the optical switch element occurs between a bright oropen state of the optical switch element in which a higher proportion ofradiant energy is transmitted and a dark or shut state of the opticalswitch element in which a smaller proportion of radiant energy istransmitted.

Radiant energy is defined as above and is understood to compriseelectromagnetic radiation in the UV-A region, VIS region andnear-infrared region. Naturally, the switch element is not equallyeffective over the complete spectrum of radiant energy as defined above.Preferably, the switch element blocks a high proportion of NIR andVIS-light in the shut state, particularly preferably a high proportionof NIR light.

Also preferred are switch elements that switch in one of the ranges VISor NIR only as well as combinations switching in one range andpermanently blocking the other, for example switching VIS andpermanently blocking NIR.

According to a preferred embodiment of the invention, the switching iseffected by a change in the physical condition of the liquid-crystallinemedium. This change in the physical condition of the liquid-crystallinemedium is temperature-dependent. Preferably, it is a phase transition.According to a particularly preferred embodiment of the invention, theswitching is effected by a phase transition of the liquid-crystallinemedium from a liquid-crystalline phase to an isotropic phase which takesplace at a particular temperature. Even more preferably, the switchingis effected by a phase transition of the liquid-crystalline medium froma nematic phase to an isotropic phase.

Typically, the liquid-crystalline medium is in the isotropic state at atemperature above the phase-transition temperature and in aliquid-crystalline, preferably nematic state at a temperature below thephase-transition temperature.

Since the switching of the device is due to a temperature-dependentchange in the physical condition of the liquid-crystalline medium, theliquid-crystalline medium represents the thermoresponsive element of theoptical switch. However, further thermoresponsive elements may bepresent.

For the use of the optical switch to regulate the radiation energy flowbetween an interior space and the environment, preferably between a roomof a building and the exterior, it is desirable that the switch operatesat a temperature which is typical for the exterior of buildings.Preferably, the switching temperature of the optical switch is between−20 and 80° C., more preferably between 10 and 60° C. and mostpreferably between 20 and 50° C.

The switching temperature is defined to be the temperature of theoptical switch. Typically, this temperature is similar to the outsideair temperature. However, under some conditions, for example underdirect exposure to sunlight, it may differ significantly from theoutside air temperature. Also, in the case of certain device setups, forexample when the optical switch is located inside of an insulated glassunit, the temperature of the optical switch may differ significantlyfrom the outside air temperature.

According to a preferred embodiment of the invention, as stated above,the switching of the optical switch is effected by a change in thephysical condition of the liquid-crystalline medium. More preferably,this change in physical condition represents a phase transition whichtakes place at a certain phase transition temperature. Preferably, thephase transition temperature is between −20 and 80° C., more preferablybetween 10 and 60° C. and most preferably between 20 and 50° C.

In a highly preferred embodiment of the present invention, the plane ofpolarisation of polarised light is rotated by the liquid-crystallinemedium by a defined value if it is in the liquid-crystalline state. Incontrast, the plane of polarisation of polarised light is not rotated bythe liquid-crystalline medium if it is in the isotropic state. It is afurther aspect of this preferred embodiment, that the directions ofpolarisation of the polarisers are not identical to each other, butrotated against each other by a defined angle.

In this preferred embodiment, the two states of the device arecharacterized as follows:

In the bright or open state, incoming light is polarised linearly by thefirst polariser. The linearly polarised light then passes through theliquid-crystalline medium in its liquid-crystalline state, which leadsto its direction of polarisation being rotated by a defined angle.

After passing the liquid-crystalline medium, the linearly polarisedlight then hits the second polariser. A defined fraction of the lighthitting the polariser is transmitted through the polariser. Preferably,there is an identity or only a relatively small divergence, mostpreferably an identity of the value by which the planes of polarisationof the two polarisers are rotated against each other and the value bywhich the plane of polarisation of the polarised light is rotated by theliquid-crystalline medium in its nematic state.

Here, the value by which the plane of polarisation of the polarisedlight is rotated by the liquid-crystalline medium is understood to bethe angle formed between the plane of polarisation before entering themedium and the plane of polarisation after leaving the medium. Thisangle can in principle be between 0° and 180°. According to this, a turnby an angle X being larger than 180° is equivalent to a turn by X minusn*180°, the integer n being chosen so that the resulting angle X′ is inthe range 0°≦X′>180°.

However, it is to be noted that the liquid-crystalline medium may causea twisting of the plane of polarisation of the polarised light passingit which has an absolute value larger than 180°. Even a rotation by morethan one complete turn (360°), for example 2¼ turns or 3¾ turns mayoccur according to the invention. However, the net value by which theplane of polarisation of polarised light is rotated from entering toleaving the liquid-crystalline medium is still in any case between 0°and 180°, as has been explained above.

Obviously, depending on the reference system used, the angle by whichthe plane of polarisation is rotated may also be represented as rangingfrom −90° to 90°, negative values meaning right-turns, positive valuesmeaning left-turns.

In the bright state, due to the small divergence between the value bywhich the planes of polarisation of the two polarisers are rotatedagainst each other and the value by which the plane of polarisation ofthe polarised light is rotated by the liquid-crystalline medium, a largefraction of the light which has passed the first polariser also passesthe second polariser.

In order for the above-described bright state to occur, it is requiredthat the liquid-crystalline medium is in its liquid-crystalline state.Typically, this is the case at a temperature below the phase-transitiontemperature. Therefore, according to this preferred embodiment, theoptical switch element is in the bright state, when it is at atemperature which is below the switching temperature.

In order for the dark transparent or shut state to occur, it is requiredthat the liquid-crystalline medium is in the isotropic state. In thiscase, incoming light is again linearly polarised by the first polariser.The polarised light then passes through the liquid-crystalline mediumbeing in its isotropic state. The liquid-crystalline medium in theisotropic state does not rotate the direction of polarisation oflinearly polarised light.

After passing the liquid-crystalline medium, the linearly polarisedlight with its direction of polarisation maintained hits the secondpolariser. The direction of polarisation of the second polariser is, asdescribed above, rotated with respect to the direction of polarisationof the first polariser, which is in this case, as explained above, alsothe direction of polarisation of the linearly polarised light hittingthe second polariser.

Due to the directions of polarisation of the polarized light and thepolariser not being coincident, but rotated with respect to each otherby a defined value which is identical to the value by which the twopolarisers are rotated against each other, only a fraction of the lightis now transmitted. The amount of light transmitted in this state issmaller than the amount of light transmitted in the bright state.

As described above, in the dark or shut state, the liquid-crystallinemedium is in its isotropic state. Typically, this is the case at atemperature above the phase-transition temperature. Therefore, accordingto this preferred embodiment, the optical switch element is in the darkor shut state, when it is at a temperature which is above the switchingtemperature.

The directions of polarisation of the two polarisers may be rotated withrespect to each other by any arbitrary value, depending on the desiredtransmission of the switch element in the dark transparent state.Preferred values are in the range of 45° to 135°, more preferred 70° to110°, most preferred 80° to 100°.

The value by which the liquid-crystalline medium in its nematic staterotates the plane of polarisation of polarised light does not have to beidentical to the value by which the directions of polarisation of thetwo polarisers are rotated with respect to each other. Preferably, thevalues are similar, with a preferred deviation of very preferably lessthan 30° and most preferably less than 20°.

The value by which the liquid-crystalline medium in its nematic staterotates the plane of polarisation of polarised light is preferably inthe range of 0° to 360°. However, values of larger than 360° may also bepresent according to the invention.

For the purpose of regulating the temperature of the interior ofbuildings, the setup described above is generally preferred. At lowtemperatures, the flow of radiant energy is allowed since the opticalswitch is in the open state. This leads to an increase in the heatuptake of the building, reducing heating costs. At high temperatures,the optical switch is in the shut state, limiting the flow of radiantenergy into the building. This decreases unwanted heat uptake at hightemperatures, reducing the costs for air conditioning.

Depending on the angle by which the two polarisers are offset againsteach other, and also depending on whether the polarisers polarise all ofthe incoming light or only a fraction of it, more or less light istransmitted through the optical switch in the shut state. With perfectpolarisers in a “crossed” position (direction of polarisation rotated by90° against each other), no light is transmitted in the shut state. Ifthe direction of polarisation of the polarisers is rotated by an angledifferent than 90°, some light is transmitted even in the shut state.Such an arrangement is desirable according to the invention.

Similarly, the amount of light which is transmitted through the opticalswitch in the open state depends, among other factors, on the efficiencyof the polarisers and on the difference between the angle by which theliquid-crystalline medium rotates the direction of polarisation oflinearly polarised light and the angle by which the directions ofpolarisation of the two polarisers are rotated against each other. Withperfect polarisers and an exact congruence of the angles of rotation, upto 50% of the light is transmitted through the device in the open stateand, ideally, 0% of the light is transmitted in the shut state.

The rejection of 50% of the light is due to the fact that a perfectlinear polariser rejects (by absorption or reflection) 50% of incomingunpolarised light. The transmittance of light through the device cantherefore be raised significantly if non-perfect polarisers are used,which may be desirable.

It should be mentioned here that numerous other combinations ofpolariser orientations and rotation of the direction of polarised lightdue to the liquid-crystal medium can be used according to the presentinvention.

Other embodiments of the present invention comprise a liquid-crystallinemedium which scatters light when it is within a first temperature rangeand which is transparent within a second temperature range, whereas thissecond temperature range may be above or below the first temperaturerange. According to another embodiment of the present invention, theliquid-crystalline medium may affect the polarisation state ofcircularly polarised light.

According to a further embodiment of the present invention, theliquid-crystalline medium represents a guest-host system whichcomprises, in addition to one or more liquid-crystalline compounds, dyemolecules or other materials which show absorptive or reflectiveproperties. According to this embodiment, the liquid-crystalline mediumprovides orientation for the dye molecules when in theliquid-crystalline state (low temperature), but does not provide suchorientation when in the isotropic state (high temperature). Since thedye molecules interact with light in a different manner depending ontheir degree of orientation, the guest-host-system showstemperature-dependent transmission properties. According to the presentinvention, when the liquid-crystalline medium represents a guest-hostsystem, it may be preferable to use only one polarizer or even nopolarizer at all in the devices according to the invention. Furthermoreaccording to the present invention, when the liquid-crystalline mediumrepresents a guest-host system, a twisted nematic orientation of theliquid-crystalline medium or a vertically aligned orientation of theliquid-crystalline medium is preferably used.

According to a preferred embodiment of the invention, the rotation ofpolarised light by the liquid-crystalline medium in theliquid-crystalline state is caused by an alignment of the molecules ofthe liquid-crystalline medium. According to the invention, thisalignment is typically effected by alignment layers which are in directcontact with the liquid-crystalline medium. Preferentially, thealignment layers represent the two outer boundaries of theliquid-crystalline medium layer. For example, two alignment layersfacing each other may be attached to the interior of the compartmentenclosing the liquid-crystalline medium. According to another preferredembodiment, the alignment layers constitute the compartment enclosingthe liquid-crystalline medium. The alignment layers may be prepared byrubbing a polymer or polymer film with a rubbing cloth, a sandpaper orsome other suitable material. Polyimide films are particularly suitablefor this, but orientation may be achieved also on other kinds ofpolymers.

According to a further preferred embodiment, the alignment layer and thepolariser layer are not separate but form one single layer. They may,for example, be glued or laminated together. The property of inducing analignment of the liquid-crystalline molecules may for example beconferred to the polariser by rubbing, scratching and/or micropatterningthe polariser layer. For details, it is referred to patent applicationUS 2010/0045924, whose disclosure is hereby incorporated by reference.

A preferred embodiment of the optical switch element according to theinvention comprises the liquid-crystalline medium within a container oftransparent material, preferably a transparent polymer or glass.Furthermore, the optical switch element comprises two or more alignmentlayers which are in direct contact with the liquid-crystalline medium.For example, the alignment layers can be attached to the inner surfaceof the above-mentioned container. According to another preferredembodiment, the inner container surface can serve as an alignment layeritself. Furthermore, the optical switch element comprises two or morepolarisers which may be present in the form of polarising foils, asdisclosed above. Further rigid or flexible layers may be present, suchas additional glass sheets, bandblock filters such as UV-blocking filmsand/or insulating layers such as low-emissivity films. According to thisembodiment of the invention, the optical switch element is rigid andcannot be bent or rolled up for storage and/or transport due to thepresence of layers of rigid material.

According to another preferred embodiment of the invention, theliquid-crystalline medium is enclosed by a flexible polymer sheet. Thisflexible polymer sheet may represent the polariser and/or the alignmentlayer. Further layers, such as described above, may be additionallypresent. For details, it is referred to patent application US2010/0045924, whose disclosure is hereby incorporated by reference.According to this embodiment, the optical switch element is flexible andcan be bent and/or rolled up.

According to another preferred embodiment of the invention, theliquid-crystalline medium has a solid or gel-like consistency. Accordingto this embodiment, a rigid container for the liquid-crystalline mediumis not required, eliminating the need for glass and/or rigid polymersheets to be present in the optical switch element. An advantage of thisembodiment of the invention is that the optical switch element is lessvulnerable to damage and can be produced in the form of thin flexiblesheets which can be rolled up. The optical switch element can then becut from this roll in any shape or size, which simplifies storage,transport and production of the device.

To obtain the above-mentioned solid or gel-like consistency of theliquid-crystalline medium, the following procedures can be usedaccording to the invention.

The liquid-crystalline medium may, for example, be embedded in the formof discrete compartments such as microdroplets of liquid-crystallinemedium, within an optically transparent medium. The opticallytransparent medium preferably is a polymeric material, particularlypreferably an isotropic thermoplastic, duroplastic or elastomericpolymer. Particularly preferably, the polymeric material is athermoplastic or elastomeric polymer.

Examples for this are NCAP-films (NCAP=nematic curvilinear alignedphases) and PDLC-films (PDLC=polymer dispersed liquid crystal). NCAPfilms may be obtained by a process in which the encapsulating polymericmaterial, for example polyvinyl alcohol, the liquid-crystalline mediumand a carrier material, such as water, are mixed thoroughly in a colloidmill. Afterwards, the carrier material is removed, for example byevaporation. A detailed procedure for the formation of NCAP-films isdescribed in U.S. Pat. No. 4,435,047.

PDLC-films, which are described for example in U.S. Pat. No. 4,688,900;WO 89/06264; EP 0272585 and Mol. Cryst. Liq. Cryst. Nonlin. Optic, 157,(1988), 427-441, may be obtained by homogeneously mixing theliquid-crystalline medium with monomers and/or oligomers which willlater react to the polymer matrix. After polymerisation, a phaseseparation is induced, in which compartments or microdroplets of liquidcrystalline medium form, which are dispersed within the polymer matrix.

According to another embodiment of the invention, the liquid-crystallinemedium is present as a continuous phase within a polymer network(PN-systems). Such systems are described in detail in EP 452460, EP313053 and EP 359146, for example. The polymer network typically has aspongy structure, in which the liquid-crystalline medium can floatfreely. According to a preferred embodiment, it is formed bypolymerisation of mono- or polyacrylate monomers.

Preferably, the liquid-crystalline medium is present in PN-systems in apercentage of more than 60%, particularly preferably in a percentage of70-95%. The polymer network systems can be prepared by inducing apolymerisation reaction in a mixture comprising the liquid-crystallinemedium and the respective monomers and/or oligomers which form thethree-dimensional polymer network. According to a preferred embodiment,the polymerisation is started by photoinitiation.

According to another embodiment of the invention, the polymer does notform a network, but is dispersed in the form of small particles withinthe liquid-crystalline medium, which is present as a continuous phase asin PN-network systems.

The liquid-crystalline media according to the present invention areparticularly suitable for use in the above-mentioned PDLC-, NCAP- andPN-systems.

Further subject of the present invention is therefore a composite systemcomprising a liquid-crystalline medium as defined above and a polymer,preferably a microporous polymer.

According to the present invention, the optical switch element can beattached to transparent windows, facades, doors or roofs of any kind,including those present in private, public and commercial buildings, incontainers for transport, storage and inhabitation and in any vehicles.Particularly preferred is the attachment to insulated glass units (IGU)or multipane windows and/or the use as an integrated element ofinsulated glass units or multipane windows. According to a preferredembodiment of the invention, the optical switch element is attached atthe outside-facing side of the window, facade, door or roof. Accordingto another preferred embodiment, the optical switch element is placed inthe interior of an IGU, where it is protected from adverse effects suchas extreme weather conditions and from degradation due to UV exposure.In an alternative embodiment, the optical switch element is attached atthe inside-facing side of the window, facade, door or roof.

According to one embodiment of the invention, the optical switch elementcovers the complete surface of the window. In this case, the controlover the radiant energy flow by the switching of the device ismaximised.

According to another embodiment of the invention, the optical switchelement covers only parts of the surface of the window, so that thereare gaps left which are not covered by the optical switch element. Thesegaps may take the form of stripes, spots and/or larger areas. This couldallow that some parts of a window can be switched between a bright stateand a dark state, whereas other parts remain bright at all times. Thisleads to the transparency of the window especially in the shut state tobe increased.

The optical switch element may be used according to the invention toregulate the radiant energy flow between an interior space and theenvironment. Particularly preferably, it is used for regulating theenergy flow in the form of VIS-light and NIR-light or VIS-light only orcombinations of regulated VIS-light and permanently blocked NIR-light.It is furthermore preferred that the optical switch element regulatesthe radiant energy flow automatically, without the need for manualcontrolling, by its capability of temperature-dependent switchingbetween an open state and a shut state. According to a particularlypreferred embodiment of the invention, the optical switch element isused to regulate the interior temperature of a building and/or avehicle.

For the purposes of the present invention, all concentrations are,unless explicitly noted otherwise, indicated in mass percent and relateto the corresponding mixture or mixture component, unless explicitlyindicated otherwise.

The clearing points of liquid-crystalline mixtures are determined incapillary tubes. A suitable instrument is Mettler Toledo FP90.Typically, liquid-crystalline mixtures show a clearing range. Accordingto our definition, the clearing point is the lowest temperature of thatrange where the whole material is still nematic.

Alternatively, clearing points of a mixture in a display can bedetermined in normally white-mode TN-cells in a microscope hot stage.The beginning of the transition from the nematic to the isotropic stateleads to black spots in the TN-cell. When heating up, the temperature atwhich such spots first occur is determined to be the clearing point.

For applications according to the present invention, long-term storagebehaviour of the liquid-crystalline media in displays is relevant. Fordetermination of the long-term storage behaviour in displays, theliquid-crystalline mixture is filled into several TN-cells with athickness of 5 to 6 μm. The TN-cells receive an end-seal, get polarisersattached for normally white mode setup and are stored for up to 1000hours in a refrigerator at a given temperature. At defined timeintervals, the TN-cells are inspected visually for dark spots indicatingcrystallisation or smectic-nematic transitions. If the TN-cells do notshow spots at the end of the testing period, the test is passed.Otherwise, the time elapsed until the first spots are detected is notedas a measure of long-term storage stability.

In the present application and especially in the following examples, thestructures of the liquid crystal compounds are represented byabbreviations, which are also called “acronyms”. Tables A to C show thestructural elements of the compounds together with their correspondingabbreviations.

All groups C_(n)H_(2n+1), C_(m)H_(2m+1), C_(p)H_(2p+1) and C_(k)H_(2k+1)are preferably straight chain alkyl groups with n, m, p and k C-atoms,respectively. All groups C_(n)H_(2n), C_(m)H_(2m), C_(p)H_(2p) andC_(k)H_(2k) are preferably (CH₂)_(n), (CH₂)_(m), (CH₂)_(p) and(CH₂)_(k), respectively; and —CH═CH— preferably is trans-respectively Evinylene. The Indices n, m, p and k preferably have a value between 1and 10.

Remark: From left side to right side in the chemical structure, theindices used are n, if only one index occurs; n and m if two indicesoccur; n, m and p if three indices occur; and n, m, p and k if fourindices occur. This nomenclature may be extended if necessary.

Therefore, a right-hand-side alkyl group —C_(n)H_(2n+1) corresponding to-n according to the acronym nomenclature (see below) may also be a group—C_(m)H_(2m+1) corresponding to -m, or a group —C_(p)H_(2p+1)corresponding to -p, or a group —C_(k)H_(2k+1) corresponding to -k,depending on the index which is chosen. The same applies for all othergroups of Table C where a letter n is used signifying an alkyl grouphaving n carbon atoms and 2n+1 hydrogen atoms or an alkylene grouphaving n carbon atoms and 2n hydrogen atoms.

Table A lists the symbols used for the ring elements, table B those forthe linking groups and table C those for the symbols for the left handand the right hand end groups of the molecules.

TABLE A Ring Elements C

P

D

Dl

A

Al

G

Gl

U

Ul

Y

M

Ml

N

Nl

Np

n3f

n3fl

Th

thl

th2f

th2fl

o2f

o2fl

Dh

K

Kl

L

Ll

F

Fl

TABLE B Linking Groups E —CH2—CH2— V —CH═CH— T —C═C— W CF₂—CF₂— B —CF═CFZ —CO—O — ZI —O—CO— X —CF═CH— XI —CH═CF— O —CH₂—O— OI —O—CH₂— Q —CF₂—O—QI —O—CF₂—

TABLE C End Groups Left hand side, used alone or in Right hand side,used alone or in combination with others combination with others -n-C_(n)H_(2n+1)— -n —C_(n)H_(2n+1) —nO— C_(n)H_(2n+1)—O— —On—O—C_(n)H_(2n+1) —V— CH₂═CH— —V CH═CH₂ —nV— C_(n)H_(2n+1)—CH═CH— —nVC_(n)H_(2n)—CH═CH₂ —Vn— CH₂═CH—C_(n)H_(2n)— —Vn CH═CHC_(n)H_(2n+1) —nVm—C_(n)H_(2n+1)—CH═CH—C_(m)H_(2m)— —nVm —C_(n)H_(2n)—CH═CH—C_(m)H_(2m+1)—N— N≡C— —N —C≡N —S— S═C═N— —S —N═C═S —F— F— —F —F —CL— Cl— —CL —Cl -M-CFH₂ -M —CFH₂ -D- CF₂H— -D —CF₂H -T- CF₃— -T —CF₃ —MO— CFH₂O— —OM —OCFH₂—DO— CF₂HO— —OD —OCF₂H —TO— CF₃O— —OT —OC F₃ -A- H—C≡C— -A —C≡C—H -nA-C_(n)H_(2n+1)—C≡C— -An —C≡C—C_(n)H_(2n+1) —NA— N≡C—C≡C— —AN —C≡C—C≡NLeft hand side, used in combination Right hand side, used in with othersonly combination with others only - . . . n . . . - —C_(n)H_(2n)— - . .. n . . . —C_(n)H_(2n)— - . . . m . . . - —CFH— - . . . M . . . —CFH— -. . . D . . . - —CF₂— - . . . D . . . —CF₂— - . . . V . . . - CH═CH— - .. . V . . . —CH═CH— - . . . Z . . . - —CO—O— - . . . Z . . . —CO—O— - .. . Zl . . . - —O—CO— - . . . Zl . . . —O—CO— - . . . K . . . - —CO— - .. . K . . . —CO— - . . . W . . . - —CF═CF— - . . . W . . . —CF═CF—wherein n and m each are integers and three points “ . . . ” indicatethat other symbols of this table may be present at the position.

TABLE D1 Illustrative Structures

AZP-n-m

CC-n-Om

CC-n-m

CC-n-Vm

CC-nV-m

CG-n-N

CG-nVm-N

CP-n-N

CP-n-m

CP-n-F

CP-n-Om

CP-nV-N

CU-n-N

CZIP-n-m

CZIP-n-N

CZIU-n-VT

CZIY-n-m

CZG-n-Om

CZG-n-OT

CZG-n-N

CZG-Vn-N

CZG-n-F

CZG-n-S

CZGI-n-m

CZIP-n-KmZIp

CZIP-n-T

CZIP-n-mOp

CZP-n-m

CZP-Vn-Om

CZP-n-OmV

CZP-n-N

CZP-n-Om

CZP-n-OmOp

CZP-n-ZIm

CZP-n-OD

CZP-n-OT

CZP-n-OmT

CZP-n-F

CZP-n-ZIV

CZP-n-OmA

CZP-n-OMm

CZP-n-mN

CZP-n-ODMT

CZP-nO-Om

CZP-nO-N

CZP-n-ZlmOp

CZU-n-AT

CZU-n-VT

CZU-n-Om

CZU-n-N

CZU-n-F

CZY-n-Om

CZY-n-m

DIZP-n-mN

DIZP-n-N

DIZIP-nVm-OpV

DZP-n-m

DZP-n-N

GZIC-n-mOp

PP-n-N

PP-n-m

PP-n-mVp

PP-nO-N

PZA-nO-m

PZC-n-N

PZG-n-N

PZG-n-F

PZP-n-N

PZP-n-m

PZP-n-Om

PZU-n-N

PZU-nVm-N

CCEP-n-m

CCP-n-m

CCP-nVm-p

CCZC-n-m

CPP-n-m

CPZIC-n-m

CPZG-n-N

CCZP-n-m

CPZP-n-N

PGU-n-F

PGP-n-m

CCPZC-n-m

CGPC-n-m

CPPC-n-m

TABLE D2 Further Illustrative Structures

Table E lists chiral dopants, which are preferably used in the liquidcrystalline media according to the present invention.

TABLE E

C 15

CB 15

CM 21

R S-811/S-811

CM 44

CM 45

CM 47

CN

R-1011/S-1011

R-2011/S-2011

R-3011/S-3011

R-4011/S-4011

R-5011/S-5011

In a preferred embodiment of the present invention the media accordingto the present invention comprise one or more compounds selected fromthe group of compounds of table E.

Table F lists stabilizers, which are preferably used in the liquidcrystalline media according to the present invention.

TABLE F

Remark: In this table “n” means an integer in the range from 1 to 12.

In a preferred embodiment of the present invention, the media accordingto the present invention comprise one or more compounds selected fromthe group of compounds of table F.

EXAMPLES

The following exemplary liquid-crystalline mixtures are listed for thepurpose of illustrating the present invention and are not to beunderstood as limiting it in any way.

The compositions of the liquid-crystalline mixtures are listed belowtogether with their clearing points and their long-term-storagebehaviour. The person skilled in the art learns from the data givenbelow which properties can be obtained with the mixtures according tothe invention. He is furthermore taught how the composition of themixtures can be modified in order to obtain the desired properties, inparticular a defined temperature of the clearing point and highlong-term stability.

Liquid crystal mixtures with the compositions listed in the followingtables are prepared, and their clearing points and long-term-storagebehaviour are determined.

As stated in the description part of the present application, theclearing point of the liquid-crystalline media according to theinvention is preferably between −20 and 80° C., more preferably between10 and 60° C. and most preferably between 20 and 50° C.

Exemplary mixtures with a relatively high clearing point (>70° C., inparticular >80° C.) are preferably used as a so-called two-bottle systemin combination with a mixture having a lower clearing point.

1) Examples for Preferred Liquid-Crystalline Medium I

Example-1 Example-2 Clearing point 66° C. 37° C. Storage stability at−40° C. >1000 h >1000 h Substance % Substance % CZP-3-O1 3 CZP-3-O1 7CZP-3-O2 4 CZP-3-O2 7 PP-2-N 8 CZP-4-O1 7 PP-3-N 7 CZP-4-O2 7 PP-4-N 10PP-2-N 8 CP-2-N 10 PP-3-N 7 CP-4-N 10 PP-4-N 10 PZP-2-N 4 CP-2-N 10PZP-3-N 3 CP-4-N 10 PZG-2-N 2 PZP-2-N 4 PZG-3-N 2 PZP-3-N 3 PZG-5-N 5PZG-2-N 2 PZG-7-N 4 PZG-3-N 2 CCZP-3-3 7 PZG-5-N 5 CCZP-3-5 7 PZG-7-N 4CCZP-4-3 7 CCZP-3-3 7 CCZP-4-5 7 sum 100 100

Example-3 Example-4 Clearing point 69.5° C. 38° C. Storage stability at−40° C. >1000 h >1000 h Substance % Substance % CZP-3-O2 7 CZP-3-O1 7CZP-3-O4 7 CZP-3-O2 7 CZP-4-O1 7 CZP-3-O4 7 CZP-4-O2 7 CZP-4-O1 7CZP-5-O1 7 CZP-4-O2 7 CZP-5-O2 7 CZP-5-O1 7 PP-2-N 4 CZP-5-O2 7 PP-3-N10 PP-2-N 4 PZP-2-N 2 PP-3-N 10 PZP-3-N 2 CP-5-3 8 PZP-1-5 12 PZP-2-N 2PZP-1O-5 10 PZP-3-N 2 CPZP-3-5 8 PZP-1-5 12 CPZP-5-3 10 PZP-3-5 11 sum100 100

Example-5 Example-6 Clearing point 67.5° C. 38.5° C. Storage stabilityat −40° C. >1000 h >1000 h Substance % Substance % CZP-3-O1 5 CZP-3-O1 5CZP-3-O2 5 CZP-3-O2 5 CZP-4-O1 5 CZP-4-O1 5 PP-3-N 9 CZP-4-O2 7 CP-3-O26 PP-3-N 9 CP-5-3 6 CP-3-O2 6 PZP-2-N 2 CP-5-3 6 PZP-2-N 2 PZP-2-N 2PZP-1-5 15 PZP-2-N 2 PZP-1O-1 16 PZP-1-5 15 CPZP-3-3 8 PZP-3-5 14CPZP-3-5 7 PZP-1O-1 16 CPZP-5-3 2 CPP-3-2 8 CPP-3-2 12 sum 100 100

2) Examples for Preferred Liquid-Crystalline Medium II

Example-7 Example-8 Clearing point 72.5° C. 35° C. Storage stability at−40° C. >1000 h >1000 h Substance % Substance % CZP-3-O2 7 CZP-3-O1 7CZP-3-O4 6 CZP-3-O2 7 CZP-4-O2 7 CZP-3-O4 7 CZP-5-O1 6 CZP-4-O2 7PZP-2-N 4 CZP-5-O1 7 PZG-2-N 5 PZP-2-N 4 PZG-3-N 5 PZG-2-N 5 PZG-5-N 10PZG-3-N 5 PZG-7-N 10 PZG-5-N 10 PZP-1-5 16 PZG-7-N 8 CPZG-3-N 4 PZP-1-516 CPZG-4-N 4 PZP-3-5 11 CPZIC-3-4 10 PZP-5-5 6 CCZIC-3-5 6 sum 100 100

Example-9 Example-10 Clearing point 71.5° C. 33° C. Storage stability at−40° C. >1000 h >1000 h Substance % Substance % CZP-3-O2 10 CZP-3-O1 6CZP-5-O1 10 CZP-3-O2 8 CP-3-N 18 CZP-4-O1 6 CP-5-N 9 CZP-5-O1 8 PZP-2-N5 CP-3-N 18 PZP-3-N 5 CP-5-N 14 PZG-2-N 4 PZG-2-N 4 PZG-3-N 4 PZG-3-N 4PZG-5-N 5 PZG-4-N 8 PZP-1O-5 9 PZG-5-N 7 CPZG-3-N 3 PZP-1-5 8 CPZG-4-N 2PZP-1O-5 9 CPZIC-3-4 8 CPZIC-3-5 8 sum 100 100

3) Examples for Preferred Liquid-Crystalline Medium III

Example-11 Example-12 Clearing point 55.5° C. 31° C. Storage stabilityat −40° C. >1000 h >1000 h Substance % Substance % CZY-3-O2 10 CZY-3-O210 CU-3-N 15 CZP-3-O1 7 CC-3-O3 10 CZP-3-O2 7 CC-5-O3 9 CU-3-N 15PZG-2-N 5 CC-3-O3 10 PZG-3-N 6 CC-5-O3 9 PZG-4-N 11 PZG-2-N 5 PZG-5-N 11PZG-3-N 6 CCZC-3-3 3 PZG-4-N 11 CCZC-3-5 3 PZG-5-N 11 CCZC-4-3 3CCZC-3-3 3 CCZC-4-5 3 CCZC-3-5 3 CCZPC-3-3 4 CCZPC-3-3 3 CCZPC-3-4 4CCZPC-3-5 3 sum 100 100

Example-13 Example-14 Clearing point 70° C. 29.5° C. Storage stabilityat −40° C. >1000 h >1000 h Substance % Substance % CZP-3-O1 5 CZP-3-O1 5CZP-3-O2 4 CZP-3-O2 4 CP-3-O1 13 CZP-4-O1 7 CP-3-O2 17 CZP-4-O2 7PZG-2-N 4 CZP-5-O1 4 PZG-3-N 4 CP-3-O1 16 PZG-5-N 7 CP-3-O2 17 CC-3-O110 PZG-2-N 4 CC-5-O1 9 PZG-3-N 4 CPZG-3-N 5 PZG-4-N 4 CPZG-4-N 4 PZG-5-N7 CPZIC-3-4 7 CC-3-O1 10 CPZIC-3-5 7 CC-5-O1 9 CPPC-3-3 4 CPZG-3-N 2 sum100 100

4) Examples for Preferred Liquid-Crystalline Medium IV

Example-15 Example-16 Clearing point 72° C. 29° C. Storage stability at−40° C. >1000 h >1000 h Substance % Substance % CZP-3-O2 4 CZP-3-O1 6CZP-4-O1 4 CZP-3-O2 4 CZP-4-O2 3 CZP-4-O1 4 CP-3-2 19 CZP-4-O2 6 DP-3-N12 CZP-5-O1 6 DP-4-N 15 CP-3-2 19 DP-5-N 13 CP-3-N 19 CPP-3-2 10 CP-3-O16 CPP-5-2 8 DP-3-N 8 CPPC-3-3 5 DP-4-N 8 CPPC-5-3 7 DP-5-N 8 CPP-5-2 6sum 100 100

Example-17 Example-18 Clearing point 71° C. 33° C. Storage stability at−40° C. >1000 h >1000 h Substance % Substance % CZP-3-O1 5 CZP-3-O1 5CZP-4-O1 6 CZP-4-O1 6 CZP-5-O1 6 CZP-5-O1 6 CP-3-N 18 CZP-3-O2 6 CP-4-N16 CZP-4-O2 6 CP-5-N 15 CP-3-N 18 CP-7-N 10 CP-4-N 16 CCEP-3-1 6 CU-3-N5 CCEP-3-3 6 CP-3-O1 20 CPP-3-2 6 CP-5-3 6 CPP-5-2 6 CPP-5-2 6 sum 100100

5) Use of Liquid-Crystalline Media in Thermoresponsive Optical SwitchElements

The mixtures 1 to 18 according to the invention are employed asliquid-crystalline media in the optical switch element according to theprocedure of US 2009/0015902.

For assembling the optical switch element, the procedure described inparagraphs [0050]-[0055] of the above-mentioned patent application isfollowed, except that instead of the mixture disclosed in theapplication (5 parts 6CB (4′-hexyl-4-cyanobiphenyl), 1.25 parts mixtureE7 and 0.008 parts 811) one of the exemplary mixtures of the presentinvention is used (examples 1-18).

With the mixtures according to the invention, thermotropic opticalswitch elements with a long operational lifetime can be obtained. Theswitch elements have a switching temperature which is close to theclearing point of the mixtures (10° C. to 80° C., which is in thepreferred operating range of the elements).

This shows that high device stability together with a controllableclearing point can be obtained with the mixtures according to theinvention.

1. Thermoresponsive optical switch element comprising aliquid-crystalline medium, which comprises one or more compounds of theformula (I)

where R¹¹,R¹² are on each occurrence, identically or differently,selected from an alkyl, alkoxy or thioalkoxy group having 1 to 10 Catoms or an alkenyl, alkenyloxy or thioalkenyloxy group having 2 to 10 Catoms, where one or more H atoms in the groups mentioned above may bereplaced by F or Cl and where one or more CH₂ groups may be replaced byO or S, or are selected from the group comprising F, Cl, CN, NCS,R¹—O—CO— and R¹—CO—O—; where R¹ is, identically or differently on eachoccurrence, an alkyl or an alkenyl group having 1 to 10 C atoms, inwhich one or more H atoms may be replaced by F or Cl; and

is selected from

and

is selected from

and Z¹¹ is selected from —CO—O— and —O—CO—; and X is on each occurrence,identically or differently, F, Cl, CN or an alkyl, alkoxy or thioalkoxygroup having 1 to 10 C atoms, where one or more H atoms in the groupsmentioned above may be replaced by F or Cl and where one or more CH₂groups may be replaced by O or S; and Y is on each occurrence,identically or differently, selected from H and X.
 2. Switch elementaccording to claim 1, characterised in that the liquid-crystallinemedium additionally comprises one or more compounds of the formula (II)

where R²¹,R²² have the meanings indicated for R¹¹ and R¹² in claim 1;and

are, identically or differently, selected from

and Z²¹ is selected from —CO—O—, —O—CO—, —CF₂O—, —OCF₂—, —CH₂CH₂—,—OCH₂—, —CH₂O— and a single bond; and with the proviso that if one of

and Z²¹ is selected from —CO—O— and —O—CO—, the other one of

must not be selected from


3. Switch element according to claim 1, characterised in that theliquid-crystalline medium additionally comprises one or more compoundsof the formulas (III) and (IV)

where R³¹,R³²,R⁴¹ and R⁴² have the meanings indicated for R¹¹ and R¹² inclaim 1; and

are on each occurrence, identically or differently, selected from

where X and Y are defined as in claim 1; and

are on each occurrence, identically or differently, selected from

where X and Y are defined as in claim 1; and Z³¹ and Z³² are on eachoccurrence, identically or differently, selected from —CO—O—, —O—CO—,—CF₂O—, —OCF₂—, —CH₂CH₂—, —OCH₂—, —CH₂O— and a single bond; and Z⁴¹, Z⁴²and Z⁴³ are on each occurrence, identically or differently, selectedfrom —CO—O—, —O—CO— and a single bond.
 4. Switch element according toclaim 1, characterised in that compounds according to formula (I) arecompounds of the following formulas (I-1) and (I-2):

where R¹¹, R¹² and X are defined as in claim
 1. 5. Switch elementaccording to claim 4, characterised in that compounds according toformula (II) are compounds of the following formulas (II-1) to (II-2)

the proviso that, for compounds according to formula (II-1), if one of

the other one of

must not be selected from


6. Switch element according to claim 3, characterised in that incompounds according to formula (III),

are on each occurrence, identically or differently, selected from


7. Switch element according to claim 6, characterised in that compoundsaccording to formula (III) are compounds of the following formulas(III-1) to (III-3)


8. Switch element according to claim 3, characterised in that incompounds according to formula (IV),

are on each occurrence, identically or differently, selected from


9. Switch element according to claim 8, characterised in that compoundsaccording to formula (IV) are compounds of the following formulas (IV-1)and (IV-2)


10. Switch element according to claim 1, characterised in that X is oneach occurrence, identically or differently, selected from F and Cl. 11.Switch element according to claim 1, characterised in that the totalconcentration of the compounds of the formula (I) is between 5 and 95%.12. Switch element according to claim 1, characterised in that the totalconcentration of the compounds of the formulas (I) and (II) is between40 and 100%.
 13. Switch element according to claim 1, characterized inthat no electrical wiring, circuitry and/or switching network ispresent.
 14. Liquid-crystalline medium comprising one or more compoundsof the formula (I)

where R¹¹,R¹² are on each occurrence, identically of differently,selected from an alkyl, alkoxy or thioalkoxy group having 1 to 10 Catoms or an alkenyl, alkenyloxy or thioalkenyloxy group having 2 to 10 Catoms, where one or more H atoms in the groups mentioned above may bereplaced by F or Cl and where one or more CH₂ groups may be replaced byO or S, or are selected from the group comprising F, Cl, CN, NCS,R¹—O—CO— and R¹—CO—O—; where R¹ is, identically or differently on eachoccurrence, an alkyl or an alkenyl group having 1 to 10 C atoms, inwhich one or more H atoms may be replaced by F or Cl; and

is selected from

is selected from

and Z¹¹ is selected from —CO—O— and —O—CO—; and X is on each occurrence,identically or differently, F, Cl, CN or an alkyl, alkoxy or thioalkoxygroup having 1 to 10 C atoms, where one or more H atoms in the groupsmentioned above may be replaced by F or Cl and where one or more CH₂groups may be replaced by O and S; and Y is on each occurrence,identically or differently, selected from H and X in a totalconcentration of 5 to 95% and at least one further compound of theformula

where R²¹,R²² have the meanings indicated for R¹¹ and R¹²; and

are, identically or differently, selected from

and Z²¹ is selected from —CO—O—, —O—CO—, CF₂O—, —OCF₂—, —CH₂CH₂—,—OCH₂—, —CH₂O— and a single bond; and with the proviso that if one of

and Z²¹ is selected from —CO—O— and —O—CO—, the other one of

must not be selected from

so that the total concentration of the compounds of the formulas (I) and(II) is between 40 and 100%.
 15. Use of a liquid-crystalline mediumaccording to claim 14 in a thermoresponsive optical switch element. 16.Composite system comprising a liquid-crystalline medium according toclaim 14 and a polymer, preferably a microporous polymer.
 17. Use of aswitch element according to claim 1 for the regulation of the flow ofradiant energy between an interior space and the environment.